The present invention relates to vehicle wheel alignment, and more particularly to vehicle wheel alignment systems which employ electro-optical transducers to measure the toe alignment of the vehicle.
Reissued U.S. Pat. No. Re33,144 to Hunter and January and U.S. Pat. No. 4,319,838 to Grossman and January each describe a wheel alignment system which uses electro-optical transducers to determine the toe alignment angles of a vehicle. FIG. 2 of each of these patents shows six angle transducers carried by support assemblies which are mounted to the vehicle wheels. FIG. 4 of U.S. Pat. No. Re33,144 and FIG. 9 of U.S. Pat. No. 4,319,838 show the geometry of this arrangement and illustrate the six angles which are directly measured. These patents further describe (see U.S. Pat. No. Re33,144 col. 7 lines 26-39, and U.S. Pat. No. 4,319,838 col. 8 line 63 to col. 9 line 12) how the toe alignment angles are computed from the angles directly measured by the angle transducers.
Equipment of this general type has been used world-wide for more than a decade. Such equipment is capable of determining the pointing or "toe" alignment angles of the wheels relative to one or more appropriate reference axes, which is sufficient to allow proper adjustment of the alignment so as to reduce tire wear and provide for safe handling.
A limitation of such systems is that the measurement transducers measure only angles and do not measure distances, and thus are incapable of measuring the actual or relative positions of the wheels. Only the relative pointing directions of the wheels can be measured. Under certain conditions, such as when wear or damage to the suspension or steering components is suspected, it would be advantageous to actually measure the locations of the wheels relative to each other, the vehicle body, frame, thrust line, or other reference frame.